The present invention relates to a culture device including a device for defoaming a culture liquid (medium) for fermentative production of useful materials by aerobic culture, and a method for controlling foams by defoaming.
Aerobic culture is frequently performed in the fermentation industry, wherein oxygen is supplied by ventilation and stirring. When a large amount of air is blown into a culture medium (liquid) containing a microorganism, which has been charged in a culture tank, foams are generally produced. When too much foam is produced, the inside of a culture tank is filled with foams, and further foaming results in an overflow into an exhaust system. Particularly when a large amount of culture liquid is used, foams flow out easily into the exhaust system.
Effervescence during culture is controlled by adding a surfactant, a silicone chemical agent and the like as an antifoaming agent (e.g., C. L. Kroll et al.: I.E.C., 48, 2190 (1956)) or by a combined use of a defoaming vane and an antifoaming agent and the like (e.g., JP-B-46-30786). These methods are associated with problems in that an antifoaming agent is difficult to control, power cost is burdensome and the productivity of a useful material in the culture becomes lower.
A different defoaming device includes the use of an electric motor that rotates a rotor at a high speed (e.g., I. H. MULLER: Process Biochem. June, 37 (1972), Japanese Utility-Model Examined Publication No. 39-36996), but a culture tank needs to be larger in size, and when a greater amount of culture liquid is used, the power cost for the electric motor grows, thereby posing a limitation on the amount of the culture liquid.
A different method includes defoaming outside the culture tank by having the foams collide with an obstruction plate and the like or using a cyclone, and returning the defoamed culture into the culture tank (JP-B-39-29800, JP-B-39-26041). This method shows lower defoaming capability, as evidenced by the presence of a lot of foams in the culture liquid returned, an overflow of foams from the cyclone and the like. After all, the amount of the culture liquid that can be charged in a culture tank does not increase, leading to a lower productivity for a practical production process.
Besides these, there is a defoaming device using ultrasonication (JP-A-5-277304, JP-A-5-317606, JP-A-7-68104, JP-A-8-196994). However, it requires a container used exclusively for defoaming, such as reserve tank and the like, and a circulating pump used exclusively for this purpose, which makes the sterilization of the defoaming device difficult and necessitates a large amount of energy for complete defoaming. Moreover, it does not function effectively in pipelines having a large diameter, because energy is obtained by reflecting ultrasonic waves to locally focus the waves. This has prevented its use for defoaming in a culture tank.
None of the aforementioned defoaming devices and foam level control methods can increase the amount of a culture liquid to 70% or more of the total volume of the culture tank, without significantly decreasing the yield of the objective product in actual production.
It is therefore an object of the present invention to provide a culture device which can increase the amount of a culture liquid to 70% or more of the total volume of a culture tank, without adversely affecting the yield of the objective product, which device is free of contamination, and which affords culture using an appropriate amount of an antifoaming agent, as well as a method for controlling foams by defoaming.
According to the present invention, it has now been found that, by mounting a foam detecting sensor and an ultrasonic oscillating horn on a vertical part of a pipeline between the above-mentioned culture tank and a liquid-vapor separating device, foams generated in the culture tank can be crushed and burst by ultrasonication, thereby increasing the liquid density of foams, and by the use of a liquid-vapor separating device mounted on a defoaming device, such as a cyclone and the like, the liquid-vapor separating efficiency can be enhanced, without adversely influencing the productivity of the objective material.
Accordingly, the present invention provides a culture device which comprises
a culture tank for aerobic fermentation culture,
a liquid-vapor separating device mounted on an exhaust outlet of the culture tank,
a foam detecting sensor mounted on at least one part of an inlet pipeline, a return pipeline and a body of the liquid-vapor separating device, and
an ultrasonic oscillation horn mounted on the inlet pipeline of the liquid-vapor separating device,
wherein the ultrasonic oscillation horn is activated in response to the detection by the sensor.
In a preferable embodiment of the present invention, the ultrasonic oscillating horn is mounted on a vertical part of the exhaust outlet pipeline of the culture tank, or on a vertical part of the inlet pipeline of the liquid-vapor separating device.
In a preferable embodiment of the present invention, the liquid-vapor separating device is a cyclone.
In a preferable embodiment of the present invention, at least one additional liquid-vapor separating device is mounted on the vapor outlet of the liquid-vapor separating device and connected to the liquid-vapor separating device.
The present invention also provides a method for controlling foams by defoaming with a culture device comprising
a culture tank for aerobic fermentation culture,
a liquid-vapor separating device mounted on an exhaust outlet of the culture tank,
a foam detecting sensor mounted on at least one part of an inlet pipeline, a return pipeline and a body of the liquid-vapor separating device, and
an ultrasonic oscillation horn mounted on the inlet pipeline of the liquid-vapor separating device,
wherein the ultrasonic oscillation horn is activated in response to the detection by the sensor.